Bolus tracking is a commonly used method in CT angiography for determining the time of arrival at an organ of inflowing contrast agent injected into a peripheral vein. This method of imaging is used primarily to produce images of arteries, such as the aorta, pulmonary artery, cerebral and carotid arteries.
Known bolus tracking methods acquire a thin image slab and update it regularly using multiple short scans. The image intensity in a user-defined area is monitored, and the diagnostic image acquisition is started when a pre-defined intensity value is reached, indicating that the bolus has arrived at the target region. This kind of method requires that a significant amount of X-ray dose is spent only to find out the correct starting time of the acquisition.
U.S. Pat. No. 7,054,406 suggests reducing the radiation dose by including in a computed tomography system an X-ray supply unit performing low-dose X-ray scans and high-dose X-ray scans for a patient in which a contrast medium has been injected. The collected X-ray projection data are reconstructed to generate image data for low-dose scans and high-dose scans. In the low-dose scans that precede the high-dose scans, plural images are obtained in succession, in which ROIs (regions of interest) are set in given positions. A CT value calculating unit calculates the CT values in the ROIs in succession, and the calculated CT values are displayed as a time-density curve. The operator observes the state in which the contrast medium flows into the ROIs, and determines the timing at which the high-dose X-ray scan is started.
Although U.S. Pat. No. 7,054,406 reduces the patient radiation dose compared to acquiring only normal (high-dose) X-ray scans, the presented system still involves a substantial radiation dose only for determining when the high-dose X-ray scan should be started. Therefore, there is a need for a bolus tracking device and method which involve a reduced radiation exposure for the patient.